As an example of packet communication in the conventional mobile communication, for instance, there is shown in the Japanese unexamined patent publication 2001-60932, “Dynamic Channel Assigning Method and Device for Asynchronous Mobile Communication System.”
In packet communication in this conventional mobile communication system, a channel for packet communication is selected between shared channel packet communication which is suitable to low traffic and individual channel packet communication which is suitable to high traffic according to amount of data to be transmitted.
In the packet communication in the conventional mobile communication system, the selection is done according to amount of data to be transmitted between the shared channel packet communication and the individual channel packet communication.
However, switching states with/without soft handover is not carried out, considering moving speed of a terminal or variation of transmission environment in the packet communication in the conventional mobile communication system, so that trials of communication are kept in a while even if the quality becomes low, and accordingly, there occurs unnecessary interference.
In a CDMA system, etc., an individual channel includes a function of soft-handover which composes signals of multiple base stations, so that it is possible to increase the quality even if the transmission path is obstructed because of shadowing, etc. such that a moving object enters into shadow of buildings. Therefore, the system is suitable to the movement at a high speed.
When a moving object does not move at a high speed and is located near a specific base station, and thus it is possible to make secure communication, it is preferable to avoid using soft handover, since interference amount can be reduced and the radio resource can be used more effectively.
In general, a shared channel is seldom provided with soft handover function; it is possible for an individual channel to avoid using soft handover when sufficient quality has been already obtained.
On the other hand, when the communication involves drastic changes in transmission environment such as movement at a high speed, it is preferable to switch to state with soft handover in order to secure the quality.
However, the possibility is high to occupy the radio resource in the state with soft handover compared with the state without soft handover, and it is desirable to switch to the state without soft handover if sufficient quality can be secured in the state without soft handover.
It is one of objects of the present invention to provide a radio communication system in which the radio resource can be used effectively by discriminating switching states with/without soft handover, considering moving speed and variation of transmission environment.